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Pneumocystis pneumonia is an endemic or epidemic disease caused by the organism Pneumocystitis carinii. Visit: Pulmonary Pathology Online Pneumocystitis carinii is an opportunistic infectious agent which is more closely related to fungi than protozoa. It was long considered to be a protozoan and was reclassified as a fungus in 1988. Incidence: Present world wide & 75% of population acquire antibody by 5 years of age. Infection occurs by inhalation and most of the infections remain latent. Reactivation with clinical disease is seen only in the setting of severe underlying immunosuppression or overwhelming infection. P. carinii is an extremely common cause of infection in patients with AIDS. Pneumocystis infections are also seen in : i) Premature infants. ii) Malnourished children with imperfect immunity. iii) Congenital immune deficiency. iv) Patients- receiving cytotoxic drugs for malignancy, cortocosteroids, & immunosuppressive drugs after transplantation. Concominant infection with other opportunistic organisms such as Aspergillus, Cryptococcus, Candida, and Cytomegalovirus has been reported. Image Link Clinical presentation: Fever ; cough ; shortness of breath and less commonly chills and chest pain. Onset of symptoms in immunosuppressed patients may be abrupt and fulminant. In AIDS patients Pneumocystis carinii pneumonia seems to present as a more subtle slowly progressive disease illness. Disease in malnourished children has an insidious onset characterized by progressive dyspnea, weight loss and failure to thrive. Pathology of Pneumocystis Pneumonia: Visit:Pulmonary Infection The infection is largely confined to the lung producing interstitial pneumonia. Rare, but well documented , examples of disseminated pneumocytosis involving the eyes, liver, and spleen have been reported. Gross: Lung is firm, rubbery & noncrepitant. Cut surface may show several firm nodules with a granular mucinous appearance. Nodular areas may be separated by spongy areas of emphysematous pulmonary parenchyma. Image Link Microscopic features: 2 stages: Trophozoites & cyst are both present in the pulmonary alveoli. Microscopically, one can identify the small trophozoites (1 to 4 micrometer in diameter) and the larger cysts (8 micrometer in diameter). H & E stain shows alveoli which are distended with honey- combed, foamy, brightly eosinophilic material . There is a scanty inflammatory infiltrate composed mainly of monocyte, occasional plasma cells and histiocytes. Image Link Special Stains: Grocott's silver stain shows black cysts in alveolar wall & exudates. It looks as round or indented (“new-moon” shape). In Giemsa stain trophozoites are visible in the alveolar exudates (round or crescent shaped & nucleated). Image Link
Diagnosis: The diagnosis of pneumocystis pneumonia requires microscopical examination in order to identify pneumocystis from a clinically relevant source such as specimens of sputum, bronchoalveolar fluid, or lung tissue, because pneumocystis cannot be cultured. If the initial specimen of induced sputum is negative for pneumocystis, then bronchoscopy with bronchoalveolar lavage should be performed. Transbronchoscopic or surgical lung biopsy is rarely needed. Further reading: Pneumocystis Pneumonia.N Engl J Med. 2004 Jun 10;350(24):2487-98. |
June 2007
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